1. Field of the Invention
This invention relates broadly to dental instruments. More particularly, this invention relates to endodontic handpieces, and especially handpieces adapted for performing root canal procedures.
2. State of the Art
The pulp filled cavity in the root of the tooth is known as the root canal. When the pulp and dentin on the root canal wall become infected, the pulp and dentin must be removed due to the severe pain the infection causes the patient. In addition to cleaning the canal of the infected dentin and pulp, the canal must be shaped to properly receive obturating material. The procedure for removing the pulp and infected dentin and shaping the canal is called a root canal procedure.
Shaping the root canal is a difficult task for even a skilled dentist as the root canal has narrow and tortuous curves. Moreover, the canals are normally less than a millimeter in diameter. It is therefore difficult to shape the canals to receive obturating material.
One method of shaping the root canal is for the dentist to hold a small cylindrical file (or reamer) in his fingers and to manually maneuver the file into the root canal; i.e., to rotate the file and to also move the file in an up and down motion such that the file enters the canal. By holding the file in his or her hand the dentist receives a high degree of tactile feedback regarding resistance of the file to entry into the canal. Resistance felt by the fingers of the dentist prompts the dentist to adjust the angle, motion, and force with which the file is moved into the canal. It will be appreciated that because of the size of the canal, the files used in the root canal procedure must also be of very small dimensions. If the narrow file is subject to excessive resistance, the file can break, leaving a broken portion in the canal and thereby complicating the root canal procedure with an additional procedure to recover the file portion. Therefore, high tactile feedback of resistance is extremely important.
However, the use of hand-held files is difficult for both the dentist and the patient. When the dentist uses a hand-held file, he or she must operate with his or her fingers within the mouth of the patient. This is uncomfortable to the dentist and patient. Moreover, the rotational movement by the fingers causes fatigue to the dentist. Furthermore, placement of the fingers of the dentist within the mouth of the patient to operate the file prevents the dentist from seeing the progress of the procedure, as the fingers block the view of the dentist.
As a result, a power driven endodontic handpiece is generally used to rotate the file, with the dentist providing up and down translation of the file by manipulation of the handpiece. A power driven endodontic handpiece generally includes an elongate shank (or handle) grippable in the hand of the dentist, a distal angle portion (angle head) which is oriented orthogonal to the shank and into which the non-operational end of files, drills, burs, and other tools are interchangeably received, and a proximal drive mechanism coupled to a power supply, e.g., AC power, a battery, or compressed air, to automatically operate the drive mechanism and rotate a dental tool secured in an angle head. As a result, root canal procedures can be performed with a powered endodontic handpiece fit with a file, rather than by manual manipulation by the dentist of a file. Moving the file via an endodontic handpiece does have certain advantages over manipulation of a file with fingers uncomfortably positioned within the mouth of a patient. The fingers of the dentist are not subject to certain stresses and, as a result, do not typically suffer from fatigue. Second, because the angle head is relatively smaller than the fingers of the dentist, the mouth of the patient is also not required to be forced open to the same degree as would otherwise be necessary. Furthermore, the size of the angle head permits the dentist to view the progress of the procedure.
However, root canal performed with a power driven endodontic handpiece also has several drawbacks. Foremost, the dentist does not receive tactile feedback when operating a powered handpiece. As a result, undesirable stresses upon the file that otherwise would be perceived by the fingertips of the dentist are not so perceived, and the file is more likely to fracture. Furthermore, due to the speeds at which powered handpieces typically operate (300 rpm or higher), the likelihood of error and ledging, i.e., the creation of an undesirable ledge at the entrance to the root canal, is increased.
Moreover, while it is fairly easy to use different dental tools when the dental tools are manipulated in the fingers (i.e., to move from a file of one size to a relatively smaller file requires nothing more than placing down the larger file and picking up the smaller file), changing from one dental tool to another with an endodontic handpiece can be relatively more complicated. In order to clearly explain the potential complications, it must first be appreciated that endodontic handpieces are provided with various coupling means to engage the dental tool to the drive mechanism. Such coupling means typically require a latching mechanism or a frictional collet mechanism. Also such coupling means add both to manufacturing complexity and the size of the angle head. Furthermore, in the prior art, the mechanisms that provide for acceptable coupling of the dental tool in the angle head have created limitations on the size of dental tool which may be used by the endodontic handpiece and have caused excessive complexity with respect to the interchange from one dental tool to another.
As an example, U.S. Pat. No. 4,449,932 to Lustig discloses an endodontic handpiece for driving a dental tool having gear teeth at one end and an operational end (e.g., a file) opposite the gear teeth. The handpiece includes a small access opening orthogonally through its distal end, thereby forming the angle head. In order that the dental tool be inserted and secured in the angle head, the dental tool must be laboriously and precisely guided though one end of the small opening and then pulled through the other end. In the case of an endodontic file, this is the equivalent of threading a needle. In addition, the required technique increases the hazard of the finger of the practitioner being punctured. Furthermore, a cover must be locked over the distal end of the handpiece to lock the dental tool in position (i.e., so that the dental tool is not pushed back through the small access opening), thereby increasing the bulk of the distal end of the handpiece. Moreover, this arrangement requires that dental tools have a operational end smaller than the gear-toothed end, thereby limiting the size, design, and types of dental tools that can be used with the handpiece.
More significantly, during the root canal procedure, the file preferably is temporarily retained in the canal for radiographic evaluation of the procedure. Thus, ease of controlled handpiece separation from the file while the file is located within the root canal is of extreme importance. This is impossible with the Lustig device and extremely difficult with existing file locking mechanisms.